Topic 4: Chemical Bonding and Structure

an ion is a charged particle. Ions form from (groups of) atoms by the loss or gain of one or more electrons

electrostatic attraction between oppositley charged ions form when opositely charged ions attract (e.g nonmetal and a metal)

have a lattice structure (3D chrystalline) • fixed arrangement of ions based on repeating unit; have low volatility • e.g. coordination number of NaCl lattice is 6 because each sodium ion surrounded by 6 chloride ions and vice versa

measure of the strength of attraction between ions in their lattice

low volatility (tendency of a substance to vaporize)

• determined by the degree to which separated particles of solute are able to form bonds/attractive forces with the solvent = solubility depends on nature of solvent (‘like dissolves like’) -ionic compounds are generally soluble in ionic/polar solvents but not in non-polar solvents

high melting and boiling points • strong electrostatic force attraction between ions • solid at room temperature • the higher the ion charge, the higher the mt and bp points

don’t conduct electricity in solid state; conduct in molten state or in an aqueous solution (due to free, delocalized electrons that can move)

BRITTLE; movement of ions of the same charge along each other causes repulsive forces to cause them to split

• reactive metal and non metal (cation and anion) 1. 8+ electronegativity difference between compounds (extent of ionic character)

electrostatic attraction between a pair of electrons and a postivley charged nuclei • sharing of electrons • nonmetal and nonmetal

a group of atoms held together by a covalent bond - contains a fixed numbef of atoms 2 atoms=diatomic= Cl2 or O2

when atoms react, they tend to achieve an outer shell with 8 electrons in order to form stability (full shell)

measure of distance between two bonded nuclei

measure of enthalpy required to break bonds strong bonds are short bonds

unsymetrical/unequal sharing of electrons • dipole; two separated opposite electric charges of a bond • can be determined by electronegativity difference ( over 0.4; polar)

when electronegativity is equal to 0; bonds between the same atoms

lewis diagrams show valence shell structures

when both shared electrons from from one atom

BeCl2, H2 and BF3 (electron deficient atoms)

because electron pairs in the same valence shells carry the same charge, they repel each other so they spread themselves as far apart as possible electron domain; all electron locations in the valence shell

stronger repulsions on lone pairs weaker repulsiosn on bonding pairs

180 2 bonding electron pairs 0 non bonding electron pairs 2 electron domains e.g. carbon dioxide

less than 120 (117) • 3 electron domains • 2 bonding, 1 non ponding electron pair e.g. silicon dioxide